The invention relates to a method and apparatus for continuous treatment of fiber material in a vertical array in general, and in particular to continuous pulp digestors having a plurality of treatment areas therein, such as impregnation, cooking, and washing areas, etc.
A conventional type of continuous digestor is shown in U.S. Pat. No. 3,380,883, and Swedish Pat. No. 334,809, shows another type of prior art digestor having a separate impregnation vessel. In practice, in a conventional continuous digestor, a feeder feeds in fiber material from a steaming vessel to the top of the digestor-- the impregnation zone thereof--via a transfer line which goes from the feeder to the digestor, and a return line back to the feeder from the top of the digestor is provided. Since the feeder is connected on one side thereof to a low pressure system-- the steaming vessel-- the temperature of the return liquid from the top of the digestor-- which is part of the high pressure system-- must not be changed any significant degree during separation of the fiber material from the transfer liquid in the digestor top. If the transfer liquid temperature does rise significantly-- as it may if liquid from the lower zones of the digestor, which is hotter than the liquid in the impregnation zone, moves by convection to the top of the digestor-- then damage to the steaming apparatus may ensue, with subsequent interruption of the operation of the digestion system. Under many circumstances it is also helpful to isolate to the extent possible the temperature and pressure conditions in each treatment zone of a vertically arranged digestor.
According to the present invention a method and apparatus are provided for minimizing heat (and pressure) transfer between treatment zones to prevent damage to steaming apparatus, or other adverse consequences. This is accomplished in general, according to the present invention, by forcing fiber material from an upper treatment area into a lower treatment area at increased velocity so that liquid from the lower treatment area may not move by convection into the upper treatment area. This may be provided in part by an area of reduced cross-section arranged between the zones to be separated.
It is the primary object of the present invention to provide a method and apparatus for the substantial segregation of the temperature and pressure conditions in adjacent zones of a vertical continuous digestor or the like. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.